α-Ketoglutaric acid-derived carbon nanodots doped with manganese as fluorescent and MRI contrast agents

Carbon nanodots (CNDs) are a class of nanomaterials under 10 nm known for their distinctive optical properties. In this work, we introduce α-ketoglutaric acid (KGA) as a novel carbon precursor for the hydrothermal synthesis of CNDs (KGA-CNDs), yielding particles with an average size of 1.9 nm. KGA's efficient manganese-binding capability facilitated the successful doping of CNDs (KGAMn-CNDs), resulting in a manganese content of 6%. The significant incorporation of transition metal points out the potential applications of manganese-doped carbon nanodots (CNDs) in magnetic resonance imaging (MRI). At a magnetic field strength of 1 Tesla, the longitudinal (r₁) and transverse (r₂) relaxivity values were 5.46 s^-1 mM^-1 and 46.83 s^-1 mM^-1, respectively, surpassing the commercial Gd-based agent Gadoterate at 0.5 Tesla (r₁ = 3.58 s^-1 mM^-1; r₂ = 21.6 s^-1 mM^-1). The ratio of transverse to longitudinal relaxivity indicates the potential of KGAMn-CNDs for T₂-weighted contrast in MRI at clinically relevant magnetic field strengths. Fluorescence imaging demonstrated that both types of CNDs displayed strong fluorescence and high photostability, thereby confirming their potential as fluorescent probes. KGAMn-CNDs exhibited dual functionality, serving as contrast agents for fluorescence and MRI. These findings highlight the potential of KGA-derived CNDs as efficient dual-mode imaging agents and establish KGA as a versatile and innovative precursor for the development of CNDs with tunable physicochemical properties.